Advanced DAQ System Development
Using NI-DAQmx
Originally presented
Thursday, August 18th
Agenda
• Streaming Data Into Your PC
– Components of Streaming
– Challenge Areas / Solutions
• Tailoring Data to Your Application
–
–
–
–
Read Strategies
Streaming to Disk Enhancements
Scaling
Virtual Channel Calibration
• Deployment Tools
– Programmatic Saves (demo)
– Simulated Devices
Agenda
• Streaming Data Into Your PC
– Components of Streaming
– Challenge Areas / Solutions
• Tailoring Data to Your Application
–
–
–
–
Read Strategies
Streaming to Disk Enhancements
Scaling
Virtual Channel Calibration
• Deployment Tools
– Programmatic Saves (demo)
– Simulated Devices
Components of Streaming
DMA
Controller
`
Components of Streaming
DMA
Controller
PCI
Bus
Buffer
32
Lo
l
ca
s
Bu
`
FIFO
FIFO
Challenge #1 (CPU Utilization)
NI-DAQmx 7.3 and Prior
NI-DAQmx 7.4 and After
Challenge #2 (Buffer Overflow)
DMA
Controller
PCI
Bus
32
Buffer
Lo
l
ca
s
Bu
`
FIFO
Solutions to Buffer Overflow
• Configure Task to Ignore Overflows
• Reduce Number of Concurrent Applications
• Increase Buffer Size, Tweak Number of Samples Per Read, Reduce
Sample Rate
• Move to Off Line Analysis
• Use Unscaled or Raw Reads
Challenge #3 (FIFO Overflow)
DMA
Controller
PCI
Bus
32
Buffer
Lo
l
ca
s
Bu
`
FIFO
Scenarios Where FIFO Overflow
Occurs
• Large Systems Where Numerous Devices are
Trying to Access the PCI Bus at the Same Time
– Unfair Arbitration Due to Topology of the Bus
– Overhead of PCI Bus Arbitration / Poor Utilization of the Bus
Once Granted
H
D2
B
D1
D1
D2
B
D3
D4
Scenarios Where FIFO Overflow
Occurs
• Devices Acquiring Continuously at Very High Rates Across
Multiple Channels
• Example:
PCI Bus Theoretical Maximum = 132 MB/s
PXI-6115 – 12 Bits, 4 Channels, 10 MS/s
2 Bytes/Sample x 4 Channels x 10 MS/s = 80 MB/s
• Solutions:
– Distribute Devices Amongst Independent Bus Segments
– Look Towards Higher Bandwidth Buses such as PCIe
– Utilize Onboard Memory to Capture Smaller Data Set of
Interest
Challenge #4 (Utilizing Onboard
Memory)
NI-DAQmx 7.3 and Prior
DMA
Controller
PCI
Bus
32
Buffer
Trigger
Lo
l
ca
s
Bu
`
FIFO
Challenge #4 (Utilizing Onboard
Memory)
NI-DAQmx 7.4 and After
DMA
Controller
PCI
Bus
32
Buffer
Lo
l
ca
s
Bu
`
Trigger
FIFO
Challenge #4 (Utilizing Onboard
Memory)
NI-DAQmx 7.3 and Prior
DMA
Controller
PCI
Bus
32
Buffer
Lo
l
ca
s
Bu
`
FIFO
Challenge #4 (Utilizing Onboard
Memory)
NI-DAQmx 7.4 and After
DMA
Controller
PCI
Bus
32
Buffer
Lo
l
ca
s
Bu
`
FIFO
Utilizing Onboard Memory Summary
• For Devices With Large Onboard Memory
– Reference triggered acquisitions are no longer limited by
PCI bandwidth
– Finite Acquisitions
• Effective Buffer = Host Buffer + Onboard Memory
33 MS
1 MS
=
Effective Buffer
32 MS
+
Buffer
FIFO
• No longer require large buffers
• Fewer page locking issues
Challenge #5 (Latency of Waveform
Updates)
DMA
Controller
PCI
Bus
32
Buffer
us
lB
ca
Lo
`
FIFO
Which Properties to Use and When?
–Only Need to Change Frequency of the Waveform
–Update Can Occur Anywhere in the Waveform Period
–Need to Update Waveform Shape or Frequency
–Update Needs to Occur at the Beginning of the Period
–Maximum Latency of One Waveform Period Desired
–Control Applications Where New Data is Constantly Being Generated
–Need Finer Grained Control of How Much Data is Written to the FIFO
Agenda
• Streaming Data Into Your PC
– Components of Streaming
– Challenge Areas / Solutions
• Tailoring Data to Your Application
–
–
–
–
Read Strategies
Streaming to Disk Enhancements
Scaling
Virtual Channel Calibration
• Deployment Tools
– Programmatic Saves (demo)
– Simulated Devices
Scaled, Unscaled, and Raw Data
Waveform
Data
Scaled
Data
Timing
And
Attributes
Scaling
Channel 1
Channel 2
Channel 2
Channel 1
Reordering
Buffer
Unscaled
Data
Raw
Data
Scaled, Unscaled, and Raw Data
Waveform
Data
Unscaled
Data
Scaled
Data
Performance / Throughput
Ease of Use
Raw
Data
Streaming to Disk Enhancements
0000100101101011
Unused
Resolution
DMA
Controller
PCI
Bus
Buffer
32
Lo
l
ca
s
Bu
`
NI PCI-6110
FIFO
Scaling
Virtual
Channel
Cal
Sensor
Units
• Typical sensors
scales
Usage
uses used
–
–
––
• Typical scale
scalesused
used
Table
Thermocouple
Linear
Full
Convert
System
unitsCalibration
– Linear
rd
• order
Ex. Gage
V topolynomial
mV
3Strain
(for SW calibration)
– Polynomial
Scale atypical sensor
Accelerometer
– Table
types
– map
Calibration: Typical Measurement
System Virtual Channel Calibration
Cable connections are
overlooked sources of
measurement error
0.4%
0.04%
0.02% Product measurement
specifications
Why Use Virtual Channel Calibration?
• Calibrate your entire measurement path
– Supplement internal calibration by accounting for errors
introduced by sensors, signal conditioning, and cabling
• Reporting capabilities
– Print channel calibration with report generation
– Built-in check for expired calibration
• Custom calibration intervals
Using Virtual Channel Calibration
• Channel
Calibration Wizard
from the DAQ
Assistant
Using Virtual Channel Calibration
• Programmatic Virtual Channel Calibration with the
DAQmx Professional Tools
Agenda
• Streaming Data Into Your PC
– Components of Streaming
– Challenge Areas / Solutions
• Tailoring Data to Your Application
–
–
–
–
Read Strategies
Streaming to Disk Enhancements
Scaling
Virtual Channel Calibration
• Deployment Tools
– Programmatic Saves (demo)
– Simulated Devices
Programmatic Save
Global
Channel
Task?
Scale?
Programmatic Save
• Examples available on ni.com as a part of the DAQmx
Professional Tools
– Visual C++, .Net, LabVIEW 7.0/7.1
• Save Scales, Global Channels, and Tasks
• Programmatically deploy systems without requiring use
of the MAX Import Wizard
• Programmatically saved objects appear in MAX and are
available for use in DAQ Assistant
Programmatic Save
Programmatic Save
• Allow Interactive Deletion?
– Allow or disallow users from deleting programmatically saved
objects using DAQ Assistant
Programmatic Save
• Allow Interactive Editing?
– Allow or disallow users from
using DAQ Assistant with
programmatically saved tasks
– When enabled, only properties
supported by the DAQ
Assistant can be modified
Disabled Behavior:
Enabled Behavior:
Demo – Cell Phone Tester Application
• Deploy Configuration
• Unit Tests
– Power consumption
– Microphone strength
Simulated Devices
• Benefits
– Run NI-DAQmx programs and
Assistant without the hardware
– Evaluate NI software with simulated
devices and data
– Explore the features of NI hardware
before purchasing
DAQmx Professional Tools
#1: Virtual Channel Calibration
#2: Data Compaction
#3: Programmatic Saves of Scales, Channels, Tasks
#4: NI-DAQmx Simulated Devices
#5: Software Events
• Tutorials and examples available for all ADEs
– Go to ni.com/info and enter “daqmxpro”
Questions?
Visit the Consultation Zone
• Discuss products and configure your application
• Get estimated costs or a quote to take with you
• Request a FREE consultation – an NI engineer visits
your office to:
– Discuss your application and specialized topics
– Demonstrate customized applications, examples, and products
• Schedule an on-site seminar at your location